Metal cutting machines, for the most part, are hydraulically operated. The cutting fluids used in such machines are generally water-based so as to control temperature while providing adequate lubrication. The hydraulic oils used in metal cutting machines, with few exceptions, have not been compatible with water-based cutting fluids, so that leakage of the former into the cutting fluids has resulted in reduced effectiveness of such fluids, leading to lost production due to the necessity of premature dumping of the cutting fluids. Thus, there has been a need for hydraulic fluids which may be used in metal cutting machines which, should they leak into the aqueous metal cutting fluids employed in such machines, do not interfere with the effectiveness of such cutting fluids.